Wideband Code Division Multiple Access (WCDMA) based Evolved High Speed Packet Access (HSPA+), Orthogonal Frequency Division Multiplexing (OFDM) based Long Term Evolution/Long Term Evolution Advanced (LTE/LTE-A), and OFDM based IEEE 802.11 systems may employ higher order modulation schemes in order to achieve high data rates. In 64-quadrature amplitude modulation (64QAM) applications, chip level equalizers may be employed to mitigate channel multipath and cancel interference.
A signal to noise and interference ratio (SINR) is a quantity used to give theoretical upper bounds of channel capacity, or the rate of information transfer, in wireless communication systems. The SINR is defined as the power of a certain signal of interest divided by the sum of the interference power from all the other interfering signals and the power of some background noise. If the power of background noise term is zero, then the SINR reduces to the signal-to-interference ratio (SIR). SINR measurements are made for various purposes, such as, for example, estimation of Channel Quality Indicator (CQI) and quality measurements for the maximum-ratio combining (MRC) of retransmissions, and are important for the operation of wireless transmit/receive units (WRTUs) and network nodes.
In 64QAM applications, the constellation points may be closely spaced and have a very small angular separation. In receiver design, it may be necessary to match filter delay through channel estimation with an equivalent delay in the signal to be processed in the receiver to avoid phase errors in the demodulated symbols.